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From: Randy Dunlap <rdunlap@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Howells <dhowells@redhat.com>,
	Hulk Robot <hulkci@huawei.com>,
	Zheng Zengkai <zhengzengkai@huawei.com>,
	Tom Rix <trix@redhat.com>,
	linux-afs@lists.infradead.org,
	Marc Dionne <marc.dionne@auristor.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] afs: fix no return statement in function returning non-void
Date: Tue, 15 Jun 2021 19:19:03 -0700	[thread overview]
Message-ID: <07d62654-15c1-29a4-c671-1669ea92510b@infradead.org> (raw)
In-Reply-To: <c2002123-795c-20ae-677c-a35ba0e361af@infradead.org>

On 6/15/21 6:38 PM, Randy Dunlap wrote:
> On 6/15/21 5:32 PM, Linus Torvalds wrote:
>> On Tue, Jun 15, 2021 at 4:58 PM Randy Dunlap <rdunlap@infradead.org> wrote:
>>>
>>> Some implementations of BUG() are macros, not functions,
>>
>> Not "some", I think. Most.
>>
>>> so "unreachable" is not applicable AFAIK.
>>
>> Sure it is. One common pattern is the x86 one:
>>
>>   #define BUG()                                                   \
>>   do {                                                            \
>>           instrumentation_begin();                                \
>>           _BUG_FLAGS(ASM_UD2, 0);                                 \
>>           unreachable();                                          \
>>   } while (0)
> 
> duh.
> 
>> and that "unreachable()" is exactly what I'm talking about.
>>
>> So I repeat: what completely broken compiler / config / architecture
>> is it that needs that "return 0" after a BUG() statement?
> 
> I have seen it on ia64 -- most likely GCC 9.3.0, but I'll have to
> double check that.

Nope, I cannot repro that now. I'll check a few more arches...

>> Because that environment is broken, and the warning is bogus and wrong.
>>
>> It might not be the compiler. It might be some architecture that does
>> this wrong. It might be some very particular configuration that does
>> something bad and makes the "unreachable()" not work (or not exist).
>>
>> But *that* is the bug that should be fixed. Not adding a pointless and
>> incorrect line that makes no sense, just to hide the real bug.


-- 
~Randy


  reply	other threads:[~2021-06-16  2:19 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-15 11:55 David Howells
2021-06-15 12:03 ` David Howells
2021-06-15 14:49 ` Linus Torvalds
2021-06-15 23:58   ` Randy Dunlap
2021-06-16  0:32     ` Linus Torvalds
2021-06-16  1:38       ` Randy Dunlap
2021-06-16  2:19         ` Randy Dunlap [this message]
2021-06-16  3:15         ` Zheng Zengkai
2021-06-16 12:56           ` Tom Rix
2021-06-16 14:34             ` Linus Torvalds
2021-06-16 16:22               ` Tom Rix
2021-06-16 16:29                 ` Linus Torvalds
2021-06-18 15:23                   ` Arnd Bergmann
2021-06-16 13:41           ` David Howells
  -- strict thread matches above, loose matches on Subject: below --
2021-03-27 12:16 Zheng Zengkai
2021-03-31  2:32 ` Zheng Zengkai
2021-04-08 14:06 ` David Howells
2021-04-19 22:31   ` Randy Dunlap
2021-05-27 19:48     ` Randy Dunlap

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